package O;use B qw(minus_c save_BEGINs);use Carp;    sub import {    my ($class, $backend, @options) = @_;    eval "use B::$backend ()";    if ($@) {	croak "use of backend $backend failed: $@";    }    my $compilesub = &{"B::${backend}::compile"}(@options);    if (ref($compilesub) eq "CODE") {	minus_c;	save_BEGINs;	eval 'CHECK { &$compilesub() }';    } else {	die $compilesub;    }}1;__END__=head1 NAMEO - Generic interface to Perl Compiler backends=head1 SYNOPSIS	perl -MO=Backend[,OPTIONS] foo.pl=head1 DESCRIPTIONThis is the module that is used as a frontend to the Perl Compiler.=head1 CONVENTIONSMost compiler backends use the following conventions: OPTIONSconsists of a comma-separated list of words (no white-space).The C<-v> option usually puts the backend into verbose mode.The C<-ofile> option generates output to B<file> instead ofstdout. The C<-D> option followed by various letters turns onvarious internal debugging flags. See the documentation for thedesired backend (named C<B::Backend> for the example above) tofind out about that backend.=head1 IMPLEMENTATIONThis section is only necessary for those who want to write acompiler backend module that can be used via this module.The command-line mentioned in the SYNOPSIS section corresponds tothe Perl code    use O ("Backend", OPTIONS);The C<import> function which that calls loads in the appropriateC<B::Backend> module and calls the C<compile> function in thatpackage, passing it OPTIONS. That function is expected to returna sub reference which we'll call CALLBACK. Next, the "compile-only"flag is switched on (equivalent to the command-line option C<-c>)and a CHECK block is registered which calls CALLBACK. Thus the mainPerl program mentioned on the command-line is read in, parsed andcompiled into internal syntax tree form. Since the C<-c> flag isset, the program does not start running (excepting BEGIN blocks ofcourse) but the CALLBACK function registered by the compilerbackend is called.In summary, a compiler backend module should be called "B::Foo"for some foo and live in the appropriate directory for that name.It should define a function called C<compile>. When the user types    perl -MO=Foo,OPTIONS foo.plthat function is called and is passed those OPTIONS (split oncommas). It should return a sub ref to the main compilation function.After the user's program is loaded and parsed, that returned sub refis invoked which can then go ahead and do the compilation, usually bymaking use of the C<B> module's functionality.=head1 AUTHORMalcolm Beattie, C<mbeattie@sable.ox.ac.uk>=cut